ADJ at n

The 'angry' group

These adjectives indicate that someone is angry about a situation or an idea.

Paul is very angry at the way he has been treated.

I was furious at the ludicrous idea of rising at 3.30 in the morning for birdsong.

The preposition at is sometimes followed by an '-ing' clause.

Benny, meanwhile, was very angry at being left virtually penniless in New York.

The noun group following the preposition at sometimes indicates a person instead of a situation. The adjectives mad and pissed are often used in this way. The adjectives angry, annoyed, and furious are sometimes used in this way. Pissed is more often used in this way in American English than in British English.